LVL Handbook EUROPE

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4. STRUCTURAL DESIGN OF LVL STRUCTURES
The shear strength of LVL is highly dependent on the di-
rection of the shear stress. In the edgewise orientation the shear
strength fv,0,edge,k is the highest. LVL-P and LVL-C strength val-
ues are quite similar at 3,2-4,5 N/mm2, but in practice LVL-C
behaves more ductile (i.e. less brittle) under loading due to
the cross veneer. In the flatwise orientation the shear strength
fv,flat,k is smaller. For LVL-P the strength fv,0,flat,k is 2-3,2 N/mm 2,
but for LVL-C it is 1,1-1,3 N/mm2 due to the cross veneers
which are in the rolling shear direction compared to the main
direction of the panel. In the across direction of the panel the
strength fv,90,flat,k is 0,6 N/mm2.
Note: Multiple-glued GLVL products have manufacturer-specific
rules for size effect in flatwise shear (reference size and size effect
parameter sflat,v).
4.3.3 Tension parallel to the grain
The following expression shall be satisfied:
σ_(t,0,d)=F_(t,0,d)/A≤f_(t,0,d) (4.9)
where
σt,0,d is the design tensile stress along the grain;
Ft,0,d is the design compressive force;
A is the cross-sectional area of the member;
ft,0,d is the design tensile strength along the grain. In
addition to kmod and γM, for LVL the design value is
dependent on the length l of the member in tension.
This is taken into consideration by a factor kl which is
defined as
k_l=(3000/l)^(s/2)≤1,1 (4.10) (EC5 3.4)
where
l is the member length in tension; and
s is the size effect parameter. For LVL-P and LVL-C strength
classes it is 0,15, but individual manufacturer-defined
values are possible.
4.3.4 Tension perpendicular to the grain
The following expression shall be satisfied:
σt,90,d ≤ ft,90,d (4.11)
where
σt,90,d is the design tensile stress perpendicular to the grain;
ft,90,d is the design tensile strength perpendicular to the grain.
Although in LVL-P the veneers are parallel to the main
direction of the product, there is a small difference between
the grain directions of the veneers. This makes the product less
sensitive to cracking and the tension strength perpendicular to
the grain edgewise of LVL-P ft,90,k = 0,5-0,8 N/mm2 is slightly
higher than solid wood or glulam ft,90,k = 0,4-0,5 N/mm2.
Figure 4.7. Tension parallel to grain of surface veneers.
Figure 4.8. Edgewise and flatwise tension perpendicular to the
grain of surface veneers.
The cross veneers of LVL-C improve the tension
strength perpendicular to the grain in edgewise direction
ft,90,k = 4-5 N/mm2 is many times better than the strength of
LVL-P. This property is an advantage especially in suspended
connections and between main beams and secondary beams
or diagonal struts.
Tension strength flatwise perpendicular to the grain of
LVL-P and LVL-C is low and it is not recommended to design
a structure so that the stresses in this direction would become
critical. The strength value in this direction is normally not de-
fined in the DoPs for LVL products, but to have an idea of the
strength level, fc,90,k,flat = ~ 0,2-0,3 N/mm2 could be used for
estimations in predesign.
4.3.5 Compression parallel to the grain
The following expression shall be satisfied:
σ_(c,0,d)=F_(c,0,d)/A≤f_(c,0,d) (4.12)
where
σc,0,d is the design compression stress along the grain;
F c,0,d is the design compressive force;
A is cross-sectional area of the member; and
F c,0,d is the design compression strength along the grain.
For LVL strength classes a separate, 20% higher fc,0,k value
has been defined for service class 1 in Table 4.5 and 4.6. The
kmod factor of Eurocode 5 is similar in SC1 and SC2, but ma-
terial testing has shown compression strength values to be dif-
ferent in SC1 and SC2. The same phenomenon is also known
for other load-bearing wood products, but the strength values
t,0,d = t,0,d ≤ t,0,d (4.9)
l = �300 �2 ≤ 1,1 (4.10) (EC5 3.4)
t,0,d = t,0,d ≤ t,0,d (4.9)
l = � 3000�2 ≤ 1,1 (4.10) (EC5 3.4)
t,90,d ≤ t,90,d (4.11)
,0, = c,0,d ≤ c,0,d
122 LVL Handbook Europe